The present invention relates to a polymer electrode used for, for example, a battery, a capacitor, an electronic device, or an electrochromic element.
Electroconducting polymers have electron conductivities and exhibit reversible reduction-oxidation reactions, and therefore the application of the polymers not only to conductive materials but also to the electrodes of secondary batteries is being studied. Especially, in the field of the secondary battery, there is a strong demand of achieving a high energy density, and therefore there have been attempt is that light-weight conducting polymers are used as active materials.
Polyaniline, which is one type of the conducting polymers, has a high stability and has excellent characteristics as an electrode active material, and therefore it has been produced as a coin-type secondary battery in commercial market. However, in the case where polyaniline is used as an electrode active material, the utility thereof is still limited to small-sized secondary batteries such as of a coin type. This is because, if polyaniline is used as the electrode active substance of a secondary battery, it is required to have an electrolyte containing anion in chemical equivalent amount at least to the battery capacitance during a charge or discharge reaction, or the volume energy density becomes low since the polymer is high in size, or the like.
In the meantime, quinone compounds such as benzoquinone, naphthoquinone and anthraquinone each exhibit a reversible reduction-oxidation reaction, and therefore each of them can be utilized as the active material of a secondary battery. Jpn. Pat. Appln. KOKAI Publications No. 55-161375 and No. 4-87258 disclose that quinone compounds are utilized as active materials of secondary batteries.
It can be expected that a quinone compound has a high capacity density due to its chemical structure; however the quinone compound itself does not have a conductivity. Therefore, in order to impart a battery capacity, it is essential that the compound should be combined with an appropriate conducting agent to make a composite. Or a quinone compound having a low molecular weight is dissolved into the liquid of an electrolyte, and therefore the cycle stability is deteriorated.
In J. Electrochem. Soc., Vol. 139, No. 1, pages 28 to 32, 1992, it is reported that a conducting polymer and a quinone compound are combined together into a composite so as to induce a synergistic effect. This document discloses that polypyrrole, which is one type of the conducting polymers, and anthraquinone sulfonic acid, which is one type of the quinone compounds, are combined together to form a composite, and such a composite will have a battery capacitor of 2 times as much or more than the case of polypyrrole formed by making electrically and chemically inactive naphthalene sulfonic acid into a composite. In this document, a thin film-like polypyrrole which is polymerized by electrolysis on 1 cm.sup.2 of an area of the electrode, and the capacity density is reported to be 118 Ah/kg (the value of the energy density is not mentioned).
There are mainly two methods for preparing a conducting polymer, that is, the chemical polymerization method and the electrolytic polymerization method. The electrolytic polymerization method has an advantage that a conducting polymer can be polymerized in a film-like manner, directly on the surface of a collecting body. However, with this method, it is difficult to uniformly synthesize an electrode of a large area. On the other hand, a conducting polymer obtained by the chemical polymerization method is generally in the form of powder, and therefore, in order to make an electrode, it is necessary to provide a step of preparing a slurry obtained by adding an electroconducting agent, a binder and the like to the electroconducting polymer, and applying the slurry onto a collecting body. In contrast, the chemical polymerization method has an advantage of being able to manufacture a large-area electrode easily.
A secondary battery having a large battery capacitance inevitably has a large electrode area, and therefore it is necessary to have an electrode of a large area.